1. Field of the Invention
The invention relates to a method and system for operating a neutral beam source for treating a substrate and, more particularly, to a method and system for creating a neutral beam and pumping a processing system utilizing a neutral beam source.
2. Description of Related Art
During semiconductor processing, plasma is often utilized to assist etch processes by facilitating the anisotropic removal of material along fine lines or within vias (or contacts) patterned on a semiconductor substrate. Furthermore, plasma is utilized to enhance the deposition of thin films by providing improved mobility of adatoms on a semiconductor substrate.
For example, during dry plasma etching, a semiconductor substrate having an overlying patterned, protective layer, such as a photoresist layer, is positioned on a substrate holder in a plasma processing system. Once the substrate is positioned within the chamber, an ionizable, dissociative gas mixture is introduced, whereby the chemical composition is specially chosen for the specific material being etched on the semiconductor substrate. As the gas is introduced, excess gases are evacuated from the plasma processing system using a vacuum pump.
Thereafter, plasma is formed when a fraction of the gas species present are ionized by electrons heated via the transfer of radio frequency (RF) power either inductively or capacitively, or microwave power using, for example, electron cyclotron resonance (ECR). Moreover, the heated electrons serve to dissociate some species of the ambient gas species and create reactant specie(s) suitable for the exposed surface etch chemistry. Once the plasma is formed, selected surfaces of the substrate are etched by the plasma.
The process is adjusted to achieve appropriate conditions, including an appropriate concentration of desirable reactant and ion populations to etch various features (e.g., trenches, vias, contacts, etc.) in the selected regions of the substrate. Such substrate materials where etching is required include silicon dioxide (SiO2), low-k dielectric materials, poly-silicon, and silicon nitride.
However, the use of plasma (i.e., electrically charged particles), itself, produces problems in the manufacture of semiconductor devices. As devices have become smaller and integration densities have increased, breakdown voltages of insulation and isolation structures therein have, in many instances, been markedly reduced, often to much less than ten volts. For example, some integrated circuit (IC) device designs call for insulators of sub-micron thicknesses.
At the same time, the reduction of the size of structures reduces the capacitance value of the insulation or isolation structures, and relatively fewer charged particles are required to develop an electric field of sufficient strength to break down insulation or isolation structures. Therefore, the tolerance of semiconductor structures for the charge carried by particles impinging on them during the manufacturing process, such as a dry plasma etching process, has become quite limited and the structures for dissipating such charges during manufacture are sometimes required, often complicating the design of the semiconductor device.
While this problem could be avoided by performing processing with neutrally charged particles, the charge of an ion or electron is the only property by which the motion of these particles can be effectively manipulated and guided. Therefore, an ion must remain in a charged state until its trajectory can be established and the energy of the ion must be sufficient that its trajectory will remain unchanged when neutralized by an electron. Even then, the trajectory may be altered and the flux of a neutral beam can be severely depleted by collisions with other particles which may or may not have been neutralized and which may have trajectories which are not precisely parallel.
As a result of this need, neutral beam sources have been developed to produce a beam of neutrally charged particles of arbitrary energy which may be as low as a few electron volts and as large as tens of thousands of electron volts or larger.